A known principle of X-ray generation comprises focusing a laser beam on a solid metal target, preferably a metal having a high atomic number, for example, gold, copper, or any other dense metal. The interaction of the laser beam and of the metal thus generates a plasma and a mono-energetic X-ray emission, which are particularly used in mammography or angiography. The target is generally placed in a vacuum enclosure, where the laser/matter interaction takes place, and is mounted on a mobile support, for example, a rotating support, so that each laser firing impacts a portion of the target which has not been impacted by a previous firing.
When the metal target has a large thickness, particularly greater than 500 nanometer, the X rays are emitted in the half-space where the laser beam propagates. It is then spoken of a “retro-emission”. However, when the metal target has a small thickness, particularly a thickness smaller than 500 nanometers, the rays are emitted in the direction of the laser beam and are accordingly emitted by the surface of the metal target opposite to that impacted by the laser beam. It is then spoken of a “transmission” emission.
Usually, thin metal targets are obtained by depositing a metal layer on a copper or plastic support, after which the substrate is removed by means of a chemical bath and/or of a plasma etching. The layer thus exposed is then washed, for example, in water or alcohol, to remove a maximum amount of impurities, after which the target is mounted on the mobile support, and the support is mounted in the enclosure.
Such a manufacturing is long and the substrate removal step is besides very delicate. It is further necessary to introduce the target and its support into the enclosure, which assumes breaking the vacuum existing therein, and then reforming the vacuum, which also takes a long time. In practice, the time of use of an X-ray emission system is very limited, and its down time is long.
Similar problems are posed for the generation of particles, for example, electrons and protons, by means of a laser firing on a thin target.